Punched component

ABSTRACT

The invention relates to a punched component comprising: a) laminating a polymer film onto a metal sheet, b) subjecting the metal sheet to a punching process, by means of which the punched component is produced, wherein a polymer film is used which is provided with a cold-flowable pressure-sensitive adhesive.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

This application is a divisional of U.S. application Ser. No.15/572,026, filed Nov. 6, 2017, which is a national stage application ofInternational Application No. PCT/EP2016/060239 filed May 6, 2016, whichclaims priority to German Patent Application No. 10 2015 107 032.4 filedMay 6, 2015, the disclosures of which are incorporated herein byreference and to which priority is claimed.

FIELD OF THE INVENTION

The invention relates to a method for manufacturing a punched componentcomprising the steps: a) laminating a polymer film onto a surface of ametal sheet, b) subjecting the metal sheet to a punching process, bymeans of which the punched component is produced. Furthermore, theinvention relates to a punched component comprising a metal sheet and apolymer film which is laminated onto a surface of the metal sheet, andso is firmly bonded to the metal sheet, the polymer film being designedsuch that it can be deep drawn.

BACKGROUND OF THE INVENTION

Punched components of the type indicated above and which are providedwith a polymer film as a protective layer are used, for example, asentrance sills for motor vehicles. They are subjected to a high degreeof wear due to the effects of weather and constant stress. Inparticular, corrosion may occur on the punched surfaces and in thecross-over regions between the metal sheet, which can be made, forexample, of aluminium or also of a Cr—Ni stainless steel, and thepolymer film. In particular, crevice corrosion and filiform corrosionoften occur.

Methods for manufacturing this type of punched component, which has asurface coating in the form of a polymer film to protect againstcorrosion, are known, for example, from WO 96/25292. The polymer film isprovided here on its upper side with a scratch-resistant layer whichserves to protect against corrosion. On the lower side of the polymerfilm which has the metal sheet a layer of hot melt adhesive is providedwhich is thermally activated upon laminating the polymer film onto themetal sheet.

The methods known from the prior art for manufacturing a punchedcomponent have proven to be of value. However, it is considered to be adisadvantage that cracking occurs during the punching process if thepolymer film can not follow the deformations of the metal substrate. Inorder to prevent cracking, the entire structure of the coatings mustfollow the deformations of the metal sheet. Until now, one has not beenable to totally guarantee this in practice because, for example, smalldiscrepancies in the anchoring of the polymer film may lead to thepolymer film being re-set, and so may lead cracking.

In particular when using hot-melt adhesive, the risk of cracking isincreased because the punching process takes place at ambienttemperature and hot melt adhesive becomes brittle in this temperaturerange.

Moreover, with a brushed metal surface an increased risk of cracking isobserved because the metal surface has a distinct fine structure due tothe brushing process. The large number of microscopically small openingsbetween the polymer film and the metal surface are weak points which maylead to cracking with corresponding stressing of the punched edge. Thisin turn leads to crevice corrosion if a crevice with a width of between0.02 mm and 0.5 mm forms, and due to lack of oxygen passivation of themetal surface can not take place. Crevice corrosion occurs with almostall metals, including Cr—Ni stainless steels. Moreover, crevicecorrosion also occurs with crevices which form between metal andplastic.

With crevice corrosion, due to the high concentration of oxygen acathodic reaction takes places at the start of the crevice, while at theend of the crevice an anodic reaction that removes metal occurs.

Filiform corrosion is manifested by thread-shaped infiltrations betweenthe coating and the metal surface. With aluminium, this type ofcorrosion, which corresponds electrochemically to crevice corrosion, isa frequently observed cause of damage.

SUMMARY OF THE INVENTION

On the basis of the prior art, it is an object of the present inventionto specify a method for manufacturing a punched component and a punchedcomponent of the type specified at the start which make it possible toavoid crevice and filiform corrosion in the punched component.

In a method for manufacturing a punched component of the type specifiedat the start, this object is achieved by a polymer film being used whichis provided with a cold-flowable pressure-sensitive adhesive on its sidepointing towards the metal sheet during the lamination process. With apunched component of the type specified at the start, the object isaccordingly achieved by the polymer film for producing the firmly bondedconnection between the metal sheet and the polymer film being providedwith a cold-flowable pressure-sensitive adhesive on its side pointingtowards the metal sheet.

According to the invention therefore, the polymer film, in particular aTPU film, is fixed by means of a cold-flowable pressure-sensitiveadhesive (PSA) to the metal sheet as a substrate. The cold-flowablepressure-sensitive adhesive has a high degree of flowability at ambienttemperature which makes it possible to draw the polymer film with thepressure-sensitive adhesive over the cut side surfaces of the metalsheet during the punching process, the arrangement of the polymer filmand the pressure-sensitive adhesive resting against the side surfaces,by means of which optimal sealing of the side surfaces is guaranteed. Inaddition, due to the transverse forces that occur during the punchingprocess, the pressure-sensitive adhesive is pushed away and passes outbetween the polymer film and the metal sheet in the region of the sidesurfaces so that the cross-over region between the polymer film and themetal sheet is sealed. The edge sealing that takes place in this way isvery thermally and mechanically resistant. As a result, by using acold-flowable pressure-sensitive adhesive, cracking between the polymerfilm and the metal sheet, and so the occurrence of crevice and filiformcorrosion are reliably avoided.

Preferably, a polyurethane, in particular thermoplastic polyurethane,which has excellent self-healing and deep drawing capabilities, is usedas the polymer film. Alternatively, polyvinyl chloride or polyethylene,for example, can also be used.

A pre-requisite for the polymer film equipped with the cold-flowablepressure-sensitive adhesive being able to close off the cut side surfaceof the metal sheet is that, in order to carry out the punching process,a stamp and a corresponding die are used which are designed such thatthere is a gap between the stamp and the die so that the polymer filmand the cold-flowable pressure-sensitive adhesive are drawn along thecut side surface of the metal sheet during the punching process beforethey are transected. The size of the gap is such here that it is smallerthan the sum of the layer thicknesses of the polymer film and thepressure-sensitive adhesive.

Generally, the surface of the metal sheet can be brushed and/or smoothedbefore the lamination in step a). The brushing serves to produce a matsurface of the metal sheet. Likewise, the surface of the metal sheetthat is to be laminated must be cleaned. In particular, it is necessaryto remove from the surface any oil remaining on the surface after thebrushing and/or smoothing.

According to one embodiment of the invention provision is made such thatduring the cleaning, oil and/or fat is burnt off of the surface, inparticular a gaseous fuel being used for the burning, to which fuelsilane is added which decomposes during the burning and forms SiO₂particles which are deposited on the surface that is to be cleaned. Theburning away of the oil from the surface of the metal sheet generallytakes place at a temperature of approximately 2000° C. Since it isdifficult to control the burning process, the burning preferably takesplace in two stages, in particular in the second burning stage a gaseousfuel to which silane is added being used for the burning. This silanedecomposes during the burning, forming SiO₂ particles which aredeposited on the surface to be cleaned. These deposits in turn formanchoring points which make it possible to print directly onto the metalsurface without applying a conversion layer lying in between.

According to one configuration of the present invention provision ismade such that after the lamination in step a) and before the punchingin step b) the polymer film is heated up. In this way the polymercrystals of the polymer film are melted in order to obtain an amorphouspolymer film. In other words, by heating, the crystallinity is reduced,by means of which the polymer film acquires a high degree ofpermeability so that solvent can penetrate into the polymer film. Thisresults in good anchoring for a subsequent process of printing onto thepolymer film.

In order to amorphise the polymer film, the heating can take place at atemperature of between 60° C. and 120° C., preferably at a temperatureof between 80° C. and 100° C., particularly preferably at a temperatureof 90° C., and for a period of 10 mins to 120 mins, preferably for aperiod of 20 mins to 60 mins, particularly preferably for a period of 30mins.

Furthermore, before or simultaneously with the punching process in stepb), the metal sheet can be subjected to an embossing process. In thisway the metal sheet is reshaped plastically according to theapplication-specific requirements.

Furthermore, before or after the punching process the polymer film canbe subjected to a printing process in order to provide the polymer filmwith a desired design. Next, the polymer film is coated with a layer ofhard material, in particular in the form of a nano paint. If the polymerfilm is not subjected to a printing process, alternatively a polymerfilm can be used which is equipped as standard with a layer of hardmaterial. Due to the layer of hard material, light cleaning of thepunched component is made possible. Moreover, the polymer film isprotected against damage due to scratches etc.

In a way known in its own right, after the punching process in step b)the punched component may be subjected to deep drawing-type re-shaping.Here, the maximum depth of the re-shaping corresponds to 1 to 10 times,preferably 5 to 10 times, particularly preferably 5 to 7 times thethickness of the metal sheet. In this way the punched component isre-shaped according to the application-specific requirements. Themaximum depth of the re-shaping is limited here by the deepdrawing-capability of the pressure-sensitive adhesive.

The metal sheet may comprise or be made of one or more of the followingmaterials: aluminium, an aluminium alloy, Cr—Ni austenitic steel.Crevice corrosion occurs in many metals, also including Cr—Ni stainless,austenitic steels. Therefore, corrosion protection according to theinvention is expedient with these materials.

Furthermore, the polymer film may comprise or be made of one or more ofthe following materials: polyvinyl chloride, polyethylene, polyurethane,in particular thermoplastic polyurethane. These materials are suitabledue to their mechanical properties such as deformation when subjected totensile stress, resilience (self-healing), maximum tearing tension, andespecially deep drawing capability, as well as theirapplication-specific properties such as good printability, good to verygood coating properties and good to very good weathering properties.Moreover, due to their polymer matrix they offer reliable diffusionprotection.

The polymer film may have a film thickness of between 1 μm and 500 μm,preferably a film thickness of between 20 μm and 250 μm, particularlypreferably a film thickness of between 30 μm and 160 μm. With such filmthicknesses very good and reproducible results are achieved.

Generally, the polymer film may have a layer of hard material, inparticular in the form of a nano paint. By means of the layer of hardmaterial, which has a low surface tension, light cleaning of the punchedcomponent is made possible. Moreover, the polymer film is protected fromdamage such as scratches etc.

Furthermore, the pressure-sensitive adhesive may comprise or be made ofa self-adhesive acrylate formulation, in particular a solvent-basedacrylate adhesive. These pressure-sensitive adhesives are characterisedby a high adhesive force and particular shear stability. Moreover, theyhave very good resistance to salted water.

Furthermore, the pressure-sensitive adhesive may be applied in one layeror in a number of layers over the polymer film. Here the polymer filmmay have a total amount of 10 g/m² to 100 g/m², preferably of 20 g/m² to60 g/m², of pressure-sensitive adhesive. Very good and reproducibleresults are achieved with this amount of pressure-sensitive adhesive.

The pressure-sensitive adhesive may have a glass transition temperatureof between 10° C. and −100° C., preferably a glass transitiontemperature of between −10° C. and 80° C., particularly preferably aglass transition temperature of between −20° C. and −50° C. Generally,pressure-sensitive adhesives have glass transition temperatures withinthis temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention are made clearby means of the following description of an embodiment of a punchedcomponent according to the invention with reference to the drawings.These show as follows:

FIG. 1 a schematic cross-sectional view of the layer structure of apunched component according to the present invention,

FIG. 2 schematically, the various stages of a punching process formanufacturing the punched component, and

FIG. 3 detail A from FIG. 2 in an enlarged illustration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 shows a punched component 1 according to a first embodiment ofthe present invention and which is protected against crevice andfiliform corrosion, the layer structure of the punched component 1 beingshown schematically in cross-section. The punched part 1 comprises ametal sheet 2 which is made of aluminium and has a thickness of 0.7 mm.

The punched component 1 further comprises a self-adhesive polymer film 3which is applied to the surface of the metal sheet 2 by lamination sothat there is a firmly bonded connection to the metal sheet 2. Thepolymer film 3 is designed such that it can be deep drawn up to 3.5 mm,is made of thermoplastic polyurethane and has a film thickness of 100μm.

In a manner that is not shown, the polymer film 3 has on its outersurface a layer of hard material (not shown) in the form of a nano paintwhich has a low surface tension and so enables light cleaning of thepunched component 1. The layer of hard material is produced by means ofmaterials that contain solvent which can diffuse 3 μm to 6 μm into thepolymer film. Therefore, the layer of hard material does not have anyeffect upon the deep drawing capability of the polymer film 3.

In order to establish the firmly bonded connection between the metalsheet 2 and the polymer film 3, the polymer film 3 is provided with acold-flowable pressure-sensitive adhesive 4, or PSA, on its sidepointing towards the metal sheet 2. Here the polymer film 3 has anamount of 40 g/m² of pressure-sensitive adhesive. This is applied in onelayer over the polymer film, is made of a solvent-based acrylateadhesive 4 and has a glass transition temperature of between −20° C. and−50° C. Due to its high adhesive force, particular shear stability andvery good resistance to salted water, solvent-based acrylate adhesive 4has proven to be of value. In the neutral salt water spray test, astandardised test method for assessing the corrosion protection effect,no changes were determined in this pressure-sensitive adhesive 4 or thepolymer film 3 after 500 hours.

With aluminium, filiform corrosion, which corresponds electrochemicallyto crevice corrosion, is a frequently observed cause of damage. Withcrevice corrosion, due to the high concentration of oxygen at the startof the crevice, a cathodic reaction occurs, whereas at the end of thecrevice an anodic reaction that removes metal takes place. The start ofthe filiform corrosion often occurs at this point. The filiformcorrosion is manifested by thread-shaped infiltrations between thecoating and the metal surface. By means of the deep drawing capabilityof the polymer film 3 and the flowability of the pressure-sensitiveadhesive 4 at ambient temperature it is ensured that during the punchingprocess the cut side surfaces of the metal sheet 2 are well covered andsealed, as will be explained further in the following.

This edge sealing has good thermal and mechanical resistance. Inaddition, small-scale mechanical damage to the polymer film 3 can beeliminated by continued flow (self-healing effect of the TPU film 3). Inthis way cracking, and so the occurrence of crevice and filiformcorrosion, may be reliably avoided. In addition, due to the thickness ofthe polymer film and of the pressure-sensitive adhesive, the edgesealing is a means of protecting against contact corrosion which occurswith a conductive connection between two differently noble metals in thepresence of an electrolyte. Furthermore, the polymer film 3 serves asprotection against pitting and selective corrosion by absorbingcorrosion-triggering particles. Pitting is triggered, for example, byabrasive dust particles, whereas selective corrosion is triggered byalloy components.

In the manufacture of the punched component 1 the surface of the metalsheet 2 is first of all roughly cleaned. Next the surface of the metalsheet 2 made of aluminium is brushed. The brushing of the surface of themetal sheet 2 takes place by means of rotating, oscillating brushes witha hard strand configuration, and serves to produce a mat surface of themetal sheet 2. Next the oil remaining on the surface of the metal sheet2 after the brushing is burnt away. The burning takes place in twostages at a temperature of approximately 2000° C. A gas to which silaneis added is used here as the fuel for the second stage of the burning,which silane decomposes with the burning, forming SiO₂ particles whichare deposited on the surface of the metal sheet 2. These SiO₂ particlesform anchoring points which make it possible to print directly onto themetal sheet, dispensing with a conversion layer.

After cleaning the surface and optionally printing onto the latter, thepolymer film 3 provided with the cold-flowable pressure-sensitiveadhesive 4 is laminated onto the metal sheet 2.

In order to obtain an amorphous polymer film 3, after lamination thepolymer film 3 is heated. The heating takes place at a temperature of90° C. and for a period of 30 minutes.

Next the metal sheet 2 is subjected to a punching process at ambienttemperature, by means of which the punching component 1 is produced. Themetal sheet 2 may be subjected to an embossing process simultaneouslywith the punching process. The punching process is shown in FIG. 2.

It is evident here that the metal sheet 2 with the polymer film 3 ispunched from the side of the metal sheet 2. During the punching processthe component to be punched out is pressed in the punch by means of astamp 5 using a corresponding die 6. During this punching or cuttingprocess the material of the metal sheet 2 is first of all elasticallydeformed by the penetrating stamp 5. As the stamp 5 penetrates furtherinto the material, the material fibres are extended further until theelasticity limit of the material is exceeded so that a plasticdeformation occurs. The material is drawn from the outside to the insideto the cutting edge of the stamp 5. In this way drawing-in curvaturesare formed on the cut part.

As the stamp 5 penetrates further the shear strength of the material isalso exceeded. The material is sheared off on the cutting edge of thedie 6 and of the stamp 5 and forms cut surfaces.

The strength of the remaining cross-section of the metal sheet iseventually so low that the material breaks.

During this punching process the polymer film 3 with thepressure-sensitive adhesive 4 is drawn along the cut side edge. Due tothe shearing effect, during the punching process the pressure-sensitiveadhesive 4 is pressed out beneath the polymer film 3 and sealing of theedge of the polymer film 3 to the metal sheet 2 additionally takesplace. By means of the punching process the formation of a new metalsurface and the pressing of the pressure-sensitive adhesive 4 take placesimultaneously. In this way the pressure-sensitive adhesive 4 is appliedideally. The formation of an amorphous Al₂O₃ layer by means of autopassivation, which could have an adverse effect upon adhesion onto themetal sheet 2, is reliably avoided by the simultaneity of the surfaceformation and the pressing of the pressure-sensitive adhesive 4. Adressing for the removal of the metal oxides, which is normal inconventional methods, is therefore not required.

After the punching process the punching component is subjected to aprinting process and is then coated with the layer of hard material inthe form of nano paint.

LIST OF REFERENCE NUMBERS

-   1 punched component-   2 metal sheet-   3 polymer film-   4 pressure-sensitive adhesive-   5 stamp-   6 die

1-13. (canceled)
 14. A punched component (1) comprising a metal sheet(2) and a polymer film (3) which is laminated onto a surface of themetal sheet (2) and is firmly bonded to the metal sheet (2), the polymerfilm (3) formed from a material that can be deep drawn, wherein thepolymer film (3) is provided with a cold-flowable pressure-sensitiveadhesive (4) in order to establish the firmly bonded connection betweenthe metal sheet (2) and the polymer film (3) on its side pointingtowards the metal sheet (2).
 15. The punched component (1) according toclaim 14, wherein the metal sheet (2) comprises or is made of one ormore of the following materials: aluminium, an aluminium alloy, Cr—Niaustenitic steel.
 16. The punched component (1) according to claim 14,wherein the polymer film (3) comprises or is made of one or more of thefollowing materials: polyvinyl chloride, polyethylene, polyurethane. 17.The punched component (1) according to claim 14, wherein the polymerfilm (3) has a film thickness of between 1 μm and 500 μm.
 18. Thepunched component (1) according to claim 14, wherein the surface of thepolymer film (3) pointing away from the metal sheet (2) is coated with alayer of hard material.
 19. The punched component (1) according to claim14, wherein the self-adhesive pressure-sensitive adhesive (4) comprisesor is made of a self-adhesive acrylate formulation.
 20. The punchedcomponent (1) according to claim 14, wherein the self-adhesivepressure-sensitive adhesive (4) is applied in one layer or in a numberof layers over the polymer film (3), and/or the polymer film (3) has atotal amount of 10 g/m2 to 100 g/m2.
 21. The punched component (1)according to claim 14, wherein the pressure-sensitive adhesive (4) has aglass transition temperature of between 10° C. and −100° C.
 22. Thepunched component according to claim 14, wherein the metal sheet (2)and/or the polymer film (3) is printed.
 23. The punched component (1)according to claim 16, wherein the polyurethane is a thermoplastic. 24.The punched component (1) according to claim 15, wherein the polymerfilm (3) comprises or is made of one or more of the following materials:polyvinyl chloride, polyethylene, polyurethane.
 25. The punchedcomponent (1) according to claim 24, wherein the polyurethane is athermoplastic.
 26. The punched component (1) according to claim 14,wherein the polymer film (3) has a film thickness of between 20 μm and250 μm.
 27. The punched component (1) according to claim 14, wherein thepolymer film (3) has a film thickness of between 30 μm and 160 μm. 28.The punched component (1) according to claim 18, wherein the hardmaterial is a nano paint.
 29. The punched component (1) according toclaim 19, wherein the self-adhesive acrylate formulation is asolvent-based acrylate adhesive.
 30. The punched component (1) accordingto claim 14, wherein the pressure-sensitive adhesive (4) has a glasstransition temperature of between −10° C. and 80° C.
 31. The punchedcomponent (1) according to claim 14, wherein the pressure-sensitiveadhesive (4) has a glass transition temperature of between −20° C. and−50° C.
 32. The punched component (1) according to claim 14, wherein theself-adhesive pressure-sensitive adhesive (4) is applied in one layer orin a number of layers over the polymer film (3), and/or the polymer film(3) has a total amount of 20 g/m2 to 60 g/m2, of pressure-sensitiveadhesive (4).